Документ взят из кэша поисковой машины. Адрес оригинального документа : http://www.atnf.csiro.au/projects/askap/techdocs/LOFAR_technology.pdf Дата изменения: Thu Jan 23 06:46:22 2003 Дата индексирования: Sat Sep 6 15:58:05 2008 Кодировка: Поисковые слова: с р р с с рер рес с с р р р р р рер р р рер

LOFAR in Australia ­ A Brief Engineering Perspective
By Dr Peter J Hall, CSIRO SKA/LOFAR Program Leader 6 November, 2002 Background LOFAR (LOw Frequency ARray) is a proposed radio telescope designed to operate in the approximate frequency range 10 - 250 MHz. It is a low-frequency complement to the Square Kilometre Array (SKA), SKA being designed to cover the range 150 MHz to above 10 GHz. In fact, at its lowest frequencies LOFAR will also have an effective collecting area of a square kilometer (1 million square metres). LOFAR is expected to be operational by 2007, while the goal for SKA is 2015. Construction costs for LOFAR and SKA are of the order of USD 100M and USD 1000M, respectively. In both cases, the instruments would be built and operated by international consortia; Australia is a founding member of the 11-participant SKA consortium and may join the USA and Europe in the LOFAR endeavour. Despite the difference in operating frequency bands, LOFAR is a true stepping stone to SKA. It will be a test-bed for many key SKA technologies, and the two instruments could advantageously share sites and infrastructure. Very importantly for Australia, LOFAR technology is more accessible to R&D groups which currently lack access to the expensive design and test facilities necessary for some SKA work. While advanced facilities will continue to be available in organizations like CSIRO, involvement in LOFAR will enable a wider Australian contribution to leading-edge radio science and will build a higher profile for Australia in SKA-related prototyping. Apart from its intrinsic synergies with SKA, LOFAR is also a logical host platform for a newly-mooted international SKA demonstrator: a large, multibeaming, radio telescope operating in the SKA frequency band. LOFAR ­ SKA Similarities Both LOFAR and SKA are geographically distributed instruments having most of their several-thousand antennas grouped into hundreds of patches, or stations. Most of the stations are located within a region a few hundreds of kilometers in extent; over half the collecting area is even more condensed, occupying only a few kilometers at the center of the array. LOFAR and SKA will: · · · Be multi-beaming radio telescopes, allowing the whole collecting area to be used for tens or hundreds of simultaneous observations (c.f. existing single -beam instruments); Attain unparalleled sensitivity and flexibility by invoking "software radio" principles in which much signal processing is done using computers or programmable processing engines; Require a network of high-capacity optical fibre data links (most likely a mix of custom-installed and third-party fibre);

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Observe outside allocated radio astronomy bands and rely partially on radio frequency interference mitigation techniques now being developed in Australia and elsewhere; Demand calibration and data processing techniques of unprecedented sophistication; and Most likely be built in remote, formally declared, radio -quiet locations.

Many SKA concepts will be effectively demonstrated by LOFAR and, with adequate planning of e.g. optical fibre and power installation, key infrastructure could be shared by the two instruments. LOFAR ­ SKA Differences Despite the similarities, LOFAR and SKA are different instruments, largely because of science goals which have dictated operation in different frequency regimes. Some of the main differences are: · · · · LOFAR and SKA antennas are quite distinct and, while the LOFAR development demands are far from trivial, the SKA challenge (particularly in terms of efficiency and frequency range) is much greater; LOFAR observing bandwidths, and hence network data rates, are 100 times smaller than SKA, meaning that LOFAR information transfer needs are more compatible with existing fibre-optic technology; LOFAR receiving systems can be much simpler than SKA, with variations on leading-edge radio-on-chip technology being feasible; and Smaller LOFAR bandwidths mean that almost all signal processing can be done digitally, using extensions of existing computing and digital sign al processing (DSP) technology.

From an engineering perspective, LOFAR is an instrument which can be built using refinements of existing technology. The application of this technology will, however, provide a platform on which to base SKA system design. Opportunities for Australia Advantages such as low population density, political stability, large land area, technological sophistication and Southern Hemisphere location combine to make Australia a suitable host for the SKA. Indeed, these factors, together with technical and site characterization work by CSIRO and a few other players, have resulted in Australia being thought of by many as the favoured SKA host. However, very recent international developments, based on a polarization in the world radio a stronomy community, have the potential to leave Australia marginalized in a contest between the USA and Europe. It can be reasonably argued that hosting LOFAR, and possibly an associated higherfrequency SKA demonstrator, would significantly increase Australia's chances of attracting SKA.

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While major players (including CSIRO) will continue to contribute directly to frontier SKA R&D, many more university and industry partners could contribute both to a world class instrument (LOFAR) and, indirectly, to emergent technologies applicable ultimately to SKA. In a number of areas these technologies have the potential to build national capability, wealth and infrastructure. In addition to astronomy and radio science community input to LOFAR, contributions by Australian commercial enterprises might include: · · · · Antenna and radio receiver development and manufacture; Photonic data transport systems, including remote area networks with capacity to support local community needs; Software for array control, signal processing and scientific data reduction; Infrastructure development, including o Project planning and management o Site preparation o Fibre installation o Provision of renewable energy sources; Assistance in the establishment and operation of an international radio -quiet reserve (which would eventually incorporate the central portions of LOFAR and SKA); and Facility operation.

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There are many potential Australian commercial participants in, for example, the consulting engineering and project management arena, the ICT area and the renewable energy sector.

Dr Peter J Hall CSIRO SKA/LOFAR Program Leader (e-mail: peter.hall@csiro.au)

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